1. Field of the Invention
The present invention relates to improvements in a method of converting image outline data representative of an outline of an image such as characters (letters and symbols) and graphical representations, into dot data representative of dots which collectively define the image, so that the image is drawn by a digital plotter, recorded by a laser printer, displayed on a CRT display device, or otherwise presented by any other suitable output device.
2. Discussion of the Prior Art
In a known method of converting an image outline data (e.g., in the form of vector data) into dot data for dot-matrix representation of an image area, a coordinated pixel screen is used such that an outline of the image area is superimposed on the pixel screen. As shown in FIG. 8, the pixel screen is defined by a plurality of parallel vertical pixel lines 50 and a plurality of parallel horizontal pixel lines 52, which cooperate to define a matrix 53 of intersections 54 corresponding to dot positions. The outline of the image area as indicated at 55 in FIG. 8 is defined by a plurality of segments. In preparing the dot data from the image outline data, the intersections or dot positions 54 which lie within the image outline superimposed on the pixel screen (matrix 53) are selected as image-dot positions as indicated at 56 in FIG. 8. The method is adapted to prepare the dot data which are representative of the thus selected image-dot positions 56 or indicative of the presence of dots at these positions.
The image area 55 is reproduced according to the prepared dot data, as a group of the dots at the image-dot positions 56, as indicated by hatched circles in FIG. 8.
In the case of an image area 58 having a relatively small width as shown in FIG. 9, for example, no dot positions 54 lie within the outline of the image area. In this case, dot data cannot be prepared, and the image area 58 is not represented by image dots. To avoid this situation, the dot data are conventionally prepared according to a special rule such that the dot positions 54 outwardly adjacent to the outline of the image area 58 are selected as the image dots 56.
However, the preparation of the dot data according to the special rule as described above requires a complicated control program for conversion of the image outline data into the corresponding dot data. The use of the special rule is not desirable. Further, the procedure to determine the image dots 56 outside the outline of the image area 58 as shown in FIG. 9 is more cumbersome and complicated than the procedure to determine the image dots 56 inside the outline of the image area 55 as illustrated in FIG. 8. In the case of FIG. 9, the preparation of the relevant dot data requires the selection of certain ones of the dot positions 54 outside the image outline 58, which meet a predetermined requirement. For instance, the predetermined requirement is a predetermined distance between the dot positions 54 and the outline (a plurality of straight segments) of the image area 58. In this case, the preparation of dot data requires a step of selecting the dot positions 54 which are located over a range of the predetermined distance, and tends to be considerably complicated.